Conventionally, the working frequency of a computer is set by manipulating jumpers or other switches on the computer main board. The jumpers are changed in accordance with instruction in a of user guide of the computer main board so as to change a CPU multiple frequency factor and to control the frequency generation of a frequency generator. This, however, may be troublesome to general consumers since most people are not familiar with such a technique, and thus although the user may follow the instruction of the user guide, it is still possible and very often that the computer user cannot perform the frequency modification operation correctly.
An incorrect setting of the working frequency may result in damage to the CPU. Therefore to overcome such a problem, some of the computer main board manufacturers provide a solution which allows the computer user to set the multiple frequency factor directly on the computer screen, similar to the general setting operation of the computer BIOS. For example, an INTEL 200 series CPU requires a working frequency of 200 MHz which is provided by multiplying the basic frequency of the CPU, which is 55.556 MHz, by a multiple frequency factor of 3. In other words, the user selects the basic frequency and the multiple frequency factor on the computer screen and the computer system automatically generates the required 200 MHz working frequency for the CPU.
Although such a solution may work, some of the general consumers may only know the working frequency and not be aware of the "basic frequency" and the "multiple frequency factor". Thus, it is still difficult for the general consumers to set the working frequency in this way.
Furthermore, the conventional way of setting the working frequency is to perform the operation under the condition that the computer is already booted. The setting operation provides a frequency information and frequency switching address signal which, after being decoded, is stored in a storage device. In response to the frequency information, the storage device generates a corresponding multiple frequency factor signal and a frequency selection signal which are applied to the CPU, and a frequency generator and reset signals are sent from a resetting unit to the CPU and the system chip set to enter hardware resetting situation. After the resetting operation, the system chip supplies a reset feedback signal to clear the previous status of the resetting unit which permits the CPU and the system chip set to operate based on the newly selected multiple frequency factor and working frequency. Although this way provides an effective switching operation between different frequencies, it requires additional parts, such as the resetting unit and the storage device. This device and unit may not be of a high cost, but would constitute a substantial cost loss to the computer main board manufacturers which usually conduct a mass production of computer main boards so that even a tiny increase of the cost for each piece of computer main board would eventually result in a major loss of money for the computer main board manufacturers.
In addition, when the computer is booted, besides setting the CPU working frequency, the computer also needs to reset several other elements on the main board, such as ISA bus and PC bus, and the associated peripheral devices, such as hard disk drive, which resetting operation returns the read/write head of the hard disk drive back to the zero track to read the information of the operation system. Clearly, with the conventional way, the peripheral device and buses have to be reset twice. However, some devices, such as ISA and PCI buses, are not capable of being continuously reset and require an interval of at least 2-3 seconds between two successive resetting operations, or else the actuator (usually an electrical motor) of the hard disk drive may not work and/or the booting process may be abnormal due to the incomplete resetting operation of the peripheral chip set. This, apparently, delays the booting procedure. In accordance with the new "instant booting" requirement, the operating system screen should be visible on the computer monitor within 20 seconds of the booting of the computer system.
Thus, in view of the fact that the conventional ways that require a significant increase of additional cost would be of less industrial value, an automatic CPU working frequency setting method is needed which is done on the original computer main board structure without adding extra parts and which may be performed in a plug-and-play fashion by making use of the I/O chip, the multiple frequency control circuit and the system logic chip that are originally provided on the computer main board. Thus a lower cost and industrially highly valuable way of automatically setting the computer working frequency may be obtained.